Place a medium saucepan over medium high heat. Add the vegetable oil, then toss in the onion and fry for 2-3 minutes until translucent.
Add beef mince and continue to fry for 3-5 minutes until browned.
Pour in the dashi stock and bring to the boil.
Add in the udon noodles and boil for a couple of minutes to cook and soften (frozen udon will take a couple more minutes). Use a chopstick to jiggle and gently loosen as they cook.
Break up the curry roux, adding in a few pieces at a time until you're happy with the thickness. Stir through gently to melt and thicken.
Serve immediately while nice and hot! Garnish with spring onion.
